how can I change the eyes and add other textures like eyebrows to this model
Select your model
Enter Edit mode. Switch to vertex mode
Select eye left using CTRL+Right click: Select 1 middle point of the eye. Click on Ctrl+"+ numpad" to grow eye selection. Then switch to front view. Press "U". Select project from view. 

You now have a separate UV from the body. Create a new material (yes in edit mode) and assign it to those vertices. From there on, create an eye texture by assigning a white blank texture, switch to texture paint interaction mode (1) and paint. Save image in the UV editor.


The rest of the body has UVs already. Click on object properties from the properties window on the VERTEX tab (triangle shape of icons)
Like this: https://streamable.com/l2di8

Thank you for your consideration in voting my answer.

BFCT_Schiller